Field of the Invention
The present invention relates to image processing of detecting an altered region in a captured image.
Description of the Related Art
There is proposed the following technique of detecting alteration of an image captured by a compact digital camera, single-lens reflex digital camera, or the like. This technique detects alteration by analyzing a pattern originally contained in a captured image or comparing the feature amounts of respective regions, without embedding additional information such as a digital watermark in the captured image. Since additional information such as a digital watermark is not embedded, this technique has an advantage capable of detecting alteration without degrading the quality of a captured image or increasing the processing time by embedding of additional information.    Literature 1: Alin C. Popescu, Hany Farid, “Exposing Digital Forgeries by Detecting Duplicated Image Regions,” TR2004-515, Dartmouth College, Computer Science.
According to the technique in literature 1, alteration (to be referred to as “internal copy” hereinafter) of copying a partial region of an image to be altered to another region of this image is detected at high accuracy by comparing the feature amounts of respective partial regions.
The technique in literature 1 detects a region altered by internal copy at once for a copy pair of an image region serving as a copy source (to be referred to as a “copy-source region” hereinafter) and an image region serving as a copy destination (to be referred to as a “copy-destination region” hereinafter). However, this technique cannot discriminate the copy-source region and copy-destination region of the copy pair. In other words, this technique cannot specify the copy-destination region which is a true altered region.